Question: Luis ate 5 slices of cake. Christopher ate 4 slices. If there were 4 slices remaining, what fraction of the cake was eaten?
Explanation: $\text{fraction of cake eaten} = \dfrac{\text{number of slices eaten}}{\text{number of slices total}}$ Since they ate 9 slices of cake with 4 slices remaining, they must have begun with 13 slices. They ate ${9}$ out of $13$ slices. They ate $\dfrac{9}{13}$ of the cake.